Page 8 - From Smart Grid to Internet of Energy

Introduction to smart grid and internet of energy systems Chapter 1 3

traditional power grid has been illustrated in Fig. 1.1 to visualize generation,
transmission, distribution, and consumption levels. This hierarchical architec-
ture is installed in a unidirectional structure allowing power flow from large and
central generators to consumers over transmission and distribution lines. The
centralized generation sources are mostly based on conventional and fossil
fuel-based plants such as thermal, diesel or combined heat and power (CHP)
cogeneration plants, nuclear power plants, hydro plants or similar generators.
The generated power is firstly increased to extra high voltage levels to prevent
transmission line losses to seriously decrease the power level.
The transmission line voltages can be at 765, 500, 345, 230, and 138 kV
depending to distances and grid codes of utilization. While the transmission
substations are required to increase the voltage levels to carry high power,
the distribution substations and transformers decrease the voltage level. The
voltage levels of distribution network vary according to load and consumer
types where substation consumers are fed by 69 and 33 kV, primary consumers
at 11 and 4 kV level, and secondary or namely residential and industrial loads
are supplied with 0.4 kV voltage level. The architecture of traditional power
grid is mostly assumed in a vertical structure to describe unidirectional power
flow. However, we describe the traditional power network horizontal since the
Smart Grid is vertical due to its multilayer architecture comprised by informa-
tion and communication technologies (ICT) layer and control and management
layer [3]. The comparison prominent grid features are compared for traditional
and Smart Grids in Table 1.1 [5]. The limited control and monitoring features
of traditional grid have forced independent system operators (ISOs) and
regional transmission operators (RTOs) to improve communication capabilities
of existing power network to obtain more flexible system. In the 1980s,
advanced metering requirements have been improved to provide averaging
on power prices and the limitations of tariff selection has been removed. In
the late 1990s, environmental concerns have increased to prevent fossil fuel-
based generation that was one of the milestone to improve distributed genera-
tion, demand side management, and decentralized control and monitoring
operations. Thus, a new grid concept researches have been intensively started.
The distributed generation and decentralized control were main drivers of
RES usage in power generation. Besides, the microgrid term has been improved
in early 2000s that aided to increase capacity and resiliency of existing power
grid. Therefore, it was possible to mention about two-way power flow and two-
way communication options in the improved power grid infrastructure that is
named as Smart Grid. The improvements have also provided self-healing
and widespread control capabilities to this new power grid due to high number
of sensor usage almost at each node and line of whole grid. Once a failure
occurred in any section of network, the sensors detect the failure and protection
system manages power flow by comprising new relaying paths for power. This
control capability is provided three major technical infrastructures of Smart
Grid that are smart infrastructure, smart management and smart control sys-
tems. The smart infrastructure definition stands for power and ICT interfaces